Metal oxide-hydrogen batteries, such as nickel oxide-hydrogen batteries, have seen use as aircraft starter batteries and in aerospace applications because they are rechargeable, have an extremely long cycle life and provide a uniform output throughout the entire discharge cycle.
In the typical nickel oxide-hydrogen battery, the battery cells are sealed in an outer pressure vessel that contains pressurized hydrogen gas. On discharge of the battery, the hydrogen gas diffuses through the electrolyte surrounding the catalyst surfaces of the negative plates and becomes disassociated to the mono-atomic form. The mono-atomic hydrogen is ionized and combines with hydroxyl ions to form water, with an electron being released in the process of forming each hydrogen ion. In addition, hydroxyl ions are formed at the positive electrode by the reaction of water with the available oxygen content of the nickel oxide. As a result of these reactions, an electron current is produced in the exterior circuit.
On recharging, the reaction is reversed, with the recharging being characterized by the regeneration of hydrogen at the negative electrode and the reoxidation of nickel at the positive electrode.
An aqueous solution of potassium hydroxide is commonly used as the electrolyte in a metal oxide-hydrogen battery. Because of the high wetability of potassium hydroxide, extreme care must be exercised to prevent capillary migration of the potassium hydroxide from the cell and possible bridging between cell modules which can cause a shorting path. To contain the electrolyte within the cell modules it has been proposed to seal each cell module in a flexible plastic bag which is impervious to the flow of the liquid electrolyte. The bag is provided with a vent which is permeable to gas flow but which is impermeable to the flow of the liquid electrolyte. With this construction, there has been need for a mechanism to electrically connect the positive and negative terminals of the cell modules without destroying the hermetically sealed characteristics of the bags.